Effect of different extraction techniques on structural components and complement fixation activity of polysaccharide fractions from Terminalia macroptera leaf

The tree Terminalia macroptera is widespread in West Africa. In traditional medicine root, stem bark and leaves have been utilized frequently in the treatment of various diseases. The leaves are used in gastritis, colic and hypertension, against fever, lepra and tuberculosis. Recently, it was confirmed that polysaccharides of certain structures modulate the immune system and intensify its defense mechanism. Three techniques for extraction of leaf polysaccharides were employed: 50 °C and 100 °C water after Soxhlet extraction (SE) with organic solvents; accelerated solvent extraction (ASE) (both organic solvents and water) and boiling water extraction (BWE). Purified polysaccharide fractions with high complement fixating activity were obtained from crude extracts by ion chromatography and gel filtration. The complement fixation ability of polysaccharide fractions were determined to have ICH₅₀ values varying between 8.8 and 86.0 µg/mL, and the molecular weights of these fractions varied between 19.8 kDa and 220.3 kDa. The polysaccharide fractions from ASE extraction showed higher complement fixation activity and molecular weights. The monosaccharide compositions and partial structure were also compared. Details in the structures differ, and the difference of the complement fixation ability may relate to the difference of structural properties and will be discussed.

Keywords: Terminalia macroptera; Soxhlet extraction; Accelerated solvent extraction; Boiling water extraction; Polysaccharide; Complement fixating activity.